The present invention relates generally to a manner by which to communicate data on a channel susceptible to distortion. More particularly, the present invention relates to apparatus, and an associated method, by which to encode data with a multidimensional code, such as a hybrid dimensional SSTC (Spherical Space-Time Code) at a sending station and by which to decode the data, once received at a receiving station. Through operation of an embodiment of the present invention, data to be communicated upon a channel susceptible to fading, or other distortion, is encoded in a manner which facilitates recovery of the informational content of the data, once received at a receiving station.
A communication system is formed, at a minimum, of a sending station and a receiving station interconnected by a communication channel. Data to be communicated by the sending station to the receiving station is converted, if necessary, into a form to permit its communication upon the communication channel. A communication system can be defined by almost any combination of sending and receiving stations, including, for instance, circuit board-positioned elements as well as more conventionally-defined communication systems used by spaced-apart users to communicate data therebetween.
When data communicated upon a communication channel is received at the receiving station, the receiving station acts upon, if necessary, the received data to recreate the informational content thereof. In an ideal communication system, the data, when received at the receiving station, is identical to the data when transmitted by the sending station. However, in an actual communication system, the data is distorted during its communication upon the communication channel. Such distortion distorts values of the data when received at the receiving station. If the distortion is significant, the informational content of the data, as transmitted, cannot be recovered.
A radio communication system is exemplary of a communication system utilized to communicate data between sending and receiving stations. In a radio communication system, the communication channel is formed of a radio communication channel. A radio communication channel is defined upon a portion of the electromagnetic spectrum. In a wireline communication system, in contrast, a physical connection extending between the sending and receiving stations is required to form the communication channel. Communication of data upon a radio communication channel is particularly susceptible to distortion due, in part, to the propagation characteristics of the radio communication channel. Data communicated on conventional wireline channels are also, however, susceptible to distortion in manners analogous to the manner by which distortion is introduced upon the data communicated in a radio communication system.
Digital communication techniques have been implemented in radio, as well as other, communication systems. Digital communication techniques generally permit the communication system in which the techniques are implemented to achiever greater communication capacity contrasted to conventional, analog communication techniques.
In a communication system which utilizes digital communication techniques, information which is to be communicated is digitized to form digital bits. The digital bits are typically formatted according to a formatting scheme. Groups of the digital bits, for instance, are positioned to form a packet of data.
Multi-path transmission of the data upon a radio, or other, communication channel introduces distortion upon the data as the data is actually communicated to the receiving station by a multiple number of paths. The data detected at the receiving station, as a result, is the combination of signal values of data communicated upon a plurality of communication paths. Intersymbol interference and Rayleigh fading causes distortion of the data. Such distortion, if not compensated for, prevents the accurate recovery of the transmitted data.
Various manners are used to compensate for the distortion introduced upon the data during its communication upon a communication path. For instance, by encoding the data, prior to its transmission, various redundancies are introduced into the data. When received at a receiving station, the redundancies are removed to recreate the informational content of the data. If portions of the data are distorted during transmission upon the communication path, the redundancies introduced upon the data increase the likelihood that the remaining portion of the data shall still permit the informational content of the data to be recovered. Generally, conventional encoding schemes are two-dimensional in nature. Higher-dimensional encoding schemes, if utilized, would increase the likelihood that data, communicated upon the channel susceptible to distortion, shall be recoverable when received at a receiving station. If the data were to be encoded using a multidimensional encoding scheme, the receiving station must correspondingly provide a manner by which to decode the multidimensionality data received thereat.
If a manner could be provided by which to multidimensionality encode data prior to its transmission upon a communication channel, and thereafter decode the multidimensionality-encoded data, improved quality of communications would be possible.
It is in light of this background information related communication of data that the significant improvements of the present invention have evolved.
The present invention, accordingly, advantageously provides apparatus, and an associated method, by which to communicate data on a channel susceptible to distortion.
Through operation of an embodiment of the present invention, data to be communicated upon a communication channel is encoded at a sending station with a hybrid dimensional SSTC (Spherical Space-Time Codes) to form an encoded sequence. During further operation of an embodiment of the present invention, once the encoded sequence is received at a receiving station, the encoded sequence of data decoded to recreate the informational content of the data communicated to the receiving station.
In one aspect of the present invention, a manner is provided by which to provide hybrid dimensional modulation of Spherical Space-Time Codes (SSTC) for a variety of fractional rate codes. Fractional code rates are achieved at reduced complexity and minimal loss in performance compared to a N-dimensional spherical code. Through operation of an embodiment of the present invention, many n/n+1 code rates are achievable which are, otherwise, not possible utilizing conventional N-dimensional spherical modulation schemes.
In another aspect of the present invention, a manner is provided by which to decode data encoded pursuant to a multidimensional trellis-based coding scheme, such as a N-dimensional Spherical Space-Time Code (SSTC) encoding scheme. An equalizer is provided capable of providing equalization operations upon an input signal applied thereto formed of an input signal set defined over any number of orthogonal dimensions, viz., the signal set forms a multidimensional signal set. Encoded data formed pursuant to a multidimensional trellis-based coding scheme is decoded pursuant to operation of apparatus provided pursuant to an embodiment of the present invention at a receiving station.
In one implementation, a manner is provided by which to encode data utilizing a hybrid dimensional modulation of spherical space-time codes at a sending station. Once encoded, the encoded data is communicated by a radio sending station upon a radio channel, thereafter to be received at a receiving station. The encoding of the data facilitates recreation of the informational content thereof to overcome the effects of distortion introduced upon the sequence when transmitted upon the communication channel. Apparatus is provided for the receiving station to decode the multidimensionality coded data received thereat. Because of the encoded nature of the data, distortion introduced thereon during communication to the receiving station is less likely to prevent recovery of the informational content of the data at the receiving station.
Branch metrics are calculated at an equalizer to determine a surviving path which defines a maximum likelihood path. During decoding operations to determine the maximum likelihood path, the similarity or distance between received signals of each sampling instant in time and all of the paths entering each state or node at the sampling time are measured. Trellis paths whose distance metrics are not a minimum for a particular node are eliminated from further consideration as a portion of a maximum likelihood path. That is to say, when two or more paths enter the same state, the one having the best metric is chosen and such path forms a surviving path. Selection of surviving paths is made for each of the states. Least-likely paths are successively eliminated at each state of the decoder operation while cumulative Hamming distances or Euclidean distances for each surviving path are calculated and recorded, thereby to be used to determine the maximum likelihood path.
New branch metrics, new reference values associated with the new branch metrics, new puncturing patterns, and new diversity combining methodologies are provided to a multidimensional Viterbi equalizer and diversity combiner provided pursuant to an embodiment of the present invention to decode spherical space-time codes.
In these and other aspects, therefore, apparatus, and an associated method, is provided for a communication system having a receiving station for receiving an encoded sequence of data formed of coordinates. Each coordinate of the sequence of data is selected from a multidimensional coordinate set. The encoded sequence communicated to the receiving station is communicated upon a communication channel. A trellis decoder decodes an indication of the encoded sequence once received at the receiving station. The trellis decoder includes a metric calculator coupled to receive indications of the encoded sequence. The metric calculator calculates branch metrics for each coordinate of the multidimensional coordinate set of which coordinates of the encoded sequence are formed. Each branch metric is formed responsive to a difference calculated between an indication of each coordinate of the encoded sequence and a reference value associated therewith. The metric calculator forms a maximum-likelihood sequence path of the multidimensional encoded sequence.
A more complete appreciation of the present invention and the scope thereof can be obtained from the accompanying drawings which are briefly summarized below, the following detailed description of the presently-preferred embodiments of the invention, and the appended claims.